Like this? https://dl.dropboxusercontent.com/u/51189815/IMG_4027.MOV
Sorry about that :( Unfortunately, that's not supposed to happen. It's supposed to remove the field when you go back to previous days.
That said, you're the second person to report this. I haven't found a fix yet because I haven't been able to reproduce the bug - it's weird.
I'm going to rewrite that part and see if this gets fixed on the next release but, I won't lie, it's gonna be a shot in the dark. Mind pinging me at john[at]dayboard.co so I can follow up when I can get this fixed? Thanks!